Addressing modes for sequential control-microprocessor, Assembly Language

The addressing modes for the sequential control transfer instructions are described below:


1. Immediate: Immediate data is a part of instruction,in this type of addressing and appear in the form of successive byte or bytes. Example: MOV AX, 0005H

2. Direct: a 16-bit memory address (offset) is directly specified In the direct addressing mode, in the instruction as a part of it. Example: MOV AX, [5000H]

3. Register:  In this mode, thedata isstored in a register and it is referred using the particular register.Except IP, All the registers may be used in this mode. Example: MOV BX, AX.

4. Register Indirect: Sometimes, the address of the memory location which contains operand or data is determined in an indirect way, by using the offset registers. This mode of addressing is called as register indirect mode.The offset address of data is in either SI or BX or Dl registeredin this specific addressing mode. The default segment is either ES or DS. The data is considered to be available at the address pointed to by the content of any of the above registers in the default data segment. Example : MOV AX, [BX]

5. Indexed: In this mode, offset of the operand is stored in one of the index registers. ES and DS are the default segments for index registers SI and Dl respectively. This mode is a special case of the above discussed register indirect addressing mode. Example 5: MOV AX, [SI]

6. Register Relative:  In this mode, the data is available at an effective address formed by adding a 16-bit or 8-bit displacement with the content of any 1 of the registers BP, BX, SI and Dl in the default (either DS or ES) segment. The instance given below explains this mode. Example: MOV AX, 50H [BX]

7. Relative Based Indexed: The effective address is formed by adding a 16 bit or 8-bit displacement with the sum of contents of any one of the base registers (BX or BP) and any 1of the index registers in the default segment. Example: MOV AX, 5 OH [BX][SI]

8. Based Indexed: The effective address of data is developedin this addressing mode, by adding content of a base register (any one of BX or BP) to the content of an index register (any one of SI or Dl). The default segment register might be ES/ DS.

9. Intransigent Direct Mode: In Intransigent Direct Mode, the address in which the control is to be transferred lies in the similar  segment in which the control transfer instruction lies and appears directly in the instruction as an immediate displacement value. The displacement value is computed relative to the content of the instruction pointer IPIn this addressing mode.

10.  Intransigent Indirect Mode: In Intransigent Indirect mode, the displacement in which the control is to be transferred is in the similar segment in which the control transfer instruction lies, but it is passed to the instruction indirectly. So, the branch address is found as the content of a register or a memory location. This addressing mode can be used in unconditional branch instructions.

11. Intersegment Direct: In Intersegment Direct mode, the address to which the control is to be transferred is in a different type of segment.  This addressing mode provides  a means of branching  from 1 code segment  to another code segment. Here, the IP and CS of the destination address are indicated directly in the instruction.

12. Intersegment Indirect:  In Intersegment  Indirect mode, the address  to which  the control  is to be transferred  lies in a different  type of segment  and  it  is  passed  to  the  instruction  indirectly, for example  contents  of  a  memory  block containing  4  bytes,  for instance   IP(LSB),  IP(MSB),  CS(LSB)  and  CS(MSB)  sequentially.  The initial address of the memory block can be referred byusing any of the addressing modes, except from the immediate mode.


Posted Date: 10/10/2012 5:35:58 AM | Location : United States

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